Exhaust gas recirculation flow control system

ABSTRACT

An exhaust gas recirculation flow control system for an internal combustion engine having valve means responsive to engine air flow and to recirculated exhaust gas flow and adapted to provide a scheduled flow control signal to an exhaust gas recirculation valve. Pressure responsive means are provided to sense engine air flow and recirculated exhaust gas flow so that these two variables may act singly or collectively through said valve means in order to provide exhaust gas recirculation to the engine&#39;&#39;s intake manifold which begins smoothly and holds at a relatively constant or scheduled fraction of the engine air flow for maximum effectiveness and minimum loss in vehicle driveability. The exhaust gas recirculation control system inhibits exhaust gas recirculation until engine air flow has increased to some predetermined value and then passes exhaust gas to the intake manifold in a modifiable proportional relationship to the engine air flow. If the exhaust gas recirculation flow tends to become too high or too low a force unbalance created within the valve means closes or opens the exhaust gas recirculation valve an amount necessary to maintain a position such that the exhaust gas recirculation flow is controlled in an increasing relationship to the increasing engine air flow. As engine air flow continues to increase a point is reached in which a force unbalance is again created within the valve means causing the exhaust gas recirculation valve to completely inhibit recirculation of exhaust gas. A temperature responsive member may also be included being operative with the valve means in order to inhibit the flow of exhaust gas at a predetermined low ambient or engine compartment temperature.

United States Patent mt Wertheimer I EXHAUST GAS RECIRCULATION FLOW CONTROL SYSTEM [75] Inventor: l-larry P. Wertheimer. Hotseheads.

I73] Assignee: The Bendix Corporation. Southl'teld.

Mich.

I22] Filed: Dec. 16. I972 l2l] Appl. No.: 3l8.l50

[52] [1.8.0. I23Ill9A [5|] Int. Cl. "12in 15/06 [58] Fleldolsearclt... Ill/9A [$6] Relerences Cited UNITED STATES PATENTS 3.507.200 4/1970 tat/ma .LSKIJI'J b/li'll ZJIIWAX 3.643.640 2/]972 Ill/I19 A 3.048.672 .Ill72 lZJ/l I! A 1.662.722 SIIWZ lZJ/l l! A J.h7$.b3.\ 7/1972 Nalajima cl al.... lZJ/l W A .7l.l.42ll NW7. Sandl'tagerl lZJ/l l) A ZIJJLIN 6H9?) \artanian lZJ/l l9 A [57] ABSTRACT An exhaust gas recirculation flow control system for June 4, 1974 an internal combustion engine having valve means responsive to engine air flow and to recirculated exhaust gm flow and adapted to provide a scheduled flow control signal to an exhaust gas recirculation valve. Pressure responsive means are provided to sense engine air flow and recirculated exhaust gas flow so that these ttvo variables may act singly or collectively through said valve means in order to provide exhaust gas recirculation to the engine's intake manifold which begins smoothly and holds at a relatively constant or scheduled fraction of the engine air flow for maximum cllectivenen and minimum loss in vehicle driveability. The exhaust gas recirculation control system inhibits exhaust gas recirculation until engine air flow has increased to some predetermined value and then passes exhaust gas to the intake manifold in a modifiable proportional relationship to the engine air llow. it the exhaust gu recirculation lloxv tends to become too high or too low a force unbalance created within the valve means closes or opens the exhaust gas recirculation valve an amount necessary to maintain a position such that the exhaust gas recirculation How is controlled in an increasing relationship to the increasing engine air flow. As engine air flow continues to increase a point is reached in which a force unbalance is again created within the valve means causing the exhaust gas recirculation valve to completzpy inhibit recirculation of exhaust gas. A temperature responsive member may also be included being operative with the valve means in order to inhibit the flow of exhaust gas at a predetcrmined low ambient or engine compartment temperature.

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EXHAUST GAS RECIRCULATION FLOW CONTROL SYSTEM FlELD OF THE INVENTION This invention relates in general to a device that aids in the reduction of engine ex haust emission pollutants. More specifically. it relates to a device that regulates the amount of exhaust gas being recirculated into an intake manif d of an internal combustion engine such that the exhaust gas recirculation begins smoothly and flovvs at a relatively constant or scheduled fraction of the engine air flow. the flovv being completely inhibited .it low ambient temperatures as well as lovv and high engine air flows in order to maintain acceptable driveabilitv.

BACKGROUND OF THE INVENTION A ma or source of atmospheric air pollution is the exha usl from automobile engines. To reduce this problem two general approaches have been taken. namely: (i l exhaust treating devices te.g. catalitic mufflers. afterhurners. etc.l and (2) engine modifications to alter combustion. The latter approach includes devices vihieh advance or retard engine spark timing. temperature responsive speed control devices. and/or type exhaust gas recirculation valves.

The present invention concerns itself with engine modification and in particular an improvement in an exhaust gas recirculation system. Exhaust gas recirculallttl'l is required in most passenger cars in order to con trol oxides of nitrogen per federal and some state exhuust emissions standards. The exhaust gas recirculation tEGRl has been implemented using simple on-off controls. With such controls. the EGR varies as a funcnon of intake manifold vacuum. not necessarily in a deorable manner. To meet the more stringent emission standards for oxides of nitrogen. EGR flow rates equiv alent to l5 percent or more of the engine's air flow will have to be used when EGR is a primary means for control of oxides of nitrogen. For maximum effectiveness consistent with acceptacle vehicle driveability. the EGR flow should begin smoothly and hold at a relatively constant or scheduled fraction of the engine air flow. and EGR should be inhibited at low ambient or engine temperatures as well as at low and high engine .1" Hours.

The conventional sparlt timing control systems generally provide good performance and fuel economy. but do not necessarily minimize the output of undesirable exhaust gas elements. Exhaust treating devices on the other hand generally minimize the output of exhaust gas elements. however. at the present state ofthe art must be used in combination with one ofthe above mentioned engine modification devices.

Other devices are ltnown such as the venturi vacuum amplifiers which attempt to maintain a degree of proportionality between the amount of EGR and total engtne air flow. Although these devices are sensitive to engine air flow there is no "feedback" from the exhaust gas recirculation system enabling adjustments to be made within the system to compensate for changes in the sensed engine variables including the EGR flow rate. Further. the venturi vacuum amplifiers require close manufacturing tolerances in order to maintain PrtlPCF Lufilltli SUMMARY OF THE lNVEh'TlON it is therefore the primary object of this invention to disclose a closed loop exhaust gas recirculation control system which achieves optimum control of exhaust gas recirculation for maximum effectiveness and minimum loss in vehicle driveability. Pursuant to this object an EGR flow control system is disclosed herein. character ized by an engine air flow responsive means operative to provide a pressure signal related to engine air flow. an exhaust gas flow responsive means operative to provide a pressure signal related to exhaust gas flow. and a pilot valve member which through a plurality of dia phragms secured thereto sums these pressure signals in order to regulate an exhaust gas recirculation valve on a proportional basis. The pilot valve is biased so as to inhibit EGR llovv at low engine air flow. and a cutoff valve 'rative with the pilot valve is included to in hibit EGR flow at high engine air flow. A temperature responsive member may be included adapted to react with the cutoff valve in order to inhibit EGR flow at a predetermined low ambient temperature. Thus. a closed loop EGR flow control system results having means responsive to internal combustion engine variables including exhaust flow and engine air flow.

it is another object of this invention to provide an EGR flow contr l system which reduces the amount of exhaust gas emissions of undesirable elements while .\lmultancously maintaining acceptable vehicle drivenbilllV.

Another object of this invention is to provide an exhaust gas recirculation flow control system wherein the amount ofexhaust gas recirculated to the engine intake manifold is regulated by a pilot valve which is responsive to engine air flow. exhaust gas flow. manifold pressure. and/or adverse temperature conditions.

It is still a further object of the present invention to disclose an exhaust gas recirculation system which is designed so that its mechanical features may be easily modified or changed to produce a scheduled relation ship between EGR flow and engine air flow which departs from proportionality.

Yet another object of this invention is to provide an economical exhaust gas recirculation flow control system which may be utilized in combination with presently available exhaust gas recirculation valves.

The above and other objects and features of the in vention will become apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings and claims which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWlNGS FIG. I is a cross sectional view of the control assem bly of the preferred embodiment of this invention.

FIG. 2 is a cross sectional view of the preferred embodiment of the exhaust gas flow sensing means and its interrelationship with the standard EGR type valve.

FIG. 3 is a schematic view of a carburetor normally associated with an internal combustion engine and illustrating the engine air flow sensing means.

FIG. 4 is a partial cross sectional view of the pilot valve member shown in FIG. I and illustrating an alternative embodiment of the invention which incorporates a temperature responsive member FIG. 5 is a block diagram of the preferred embodiment of my exhaust gas recirculation flow control systent H0. 6 graphically illustrates the test results of my in- \entton as applied to an existing internal combustion engine.

FIG. 7 is an alternative embodiment of the exhaust gas flow sensing means.

DETAlLED DESCRIPTION OF THE DRAWINGS The exhaust gas recirculation flow control system according to the invention is comprised of the engine air llow sensing means shown in FIG. 3. the exhaust gas llow sensing means 30 shown in FIG. 2. and the control assembly 20 including the pilot valve member and its related structure shown in FIG. I which controls the exhaust gas recirculation tEGR) valve to shown in FIG. 2. An example ofa temperature responsive memher which may be used in combination with the insentise system is shown in FIG. 4. The interrelationship of the various system components is illustrated by the block diagram shown in FIG. 5.

Referring to H0. 3 a carburetor 4] is shown as being of the down draft type and having the usual air-fuel induction passage 45 with an atmospheric air inlet 44 at ne end and connected to the engine intake manifold 47 at the opposite end. Passage 5 contains the usual fixed area venturi 42 and a throttle valve 46. The latter is rotatably mounted on a part of the carburetor body across passage 45 in a manner to control the flow ofain fuel mixture into the intalte manifold. Fuel would be inducted in the usual manner from a nozzle. not shown. projecting into or adjacent venturi 42. in a ltnown manllLI.

Throttle valve 6 is shown in its engine idle speed pootton essentially closing induction passage 45 and is rt tatablc to a nearly vertical position essentially unblockmg passage 45. A port 49 is provided in the throat of ctttuti 42 which in combination with the venturi 42 .ind a passage 48 mounted adjacent to port 49 comprise the engine air flow sensing means. It is to be understood that the pressure or vacuum level at venturi port 49 is .t function of the total air flow passing through venturi 42. That is. engine air flow is regulated by the relative osition ofthrottle valve 4-6. As the throttle valve opens .rir flow increases which in turn causes the air pressure at port 49 to decrease with respect to atmospheric pres- \u re. or pressure at an upstream stagnation point which is not shown. The "vacuum" which is created at venturi port 9 may be termed a pressure signal which for puroses of discussion we will label as 8.. Pressure signal S, is communicated to the pilot valve housing 2! shown In FIG. 1 through passage member 48. The cross sec tional area of the throat of the venturi 42 is designated .it A The cross sectional area A. is a design parameter whlCl'l must be known since the disckised system regulates EGR flow on either a scheduled or proportional relationship with the air flow which passes through this ortt'tce.

A sparlt port 43 may be provided at a point just above the idle position of throttle valve 46. to be traversed by the throttle valve during its opening or part throttle movement. The vacuum level at sparlt port 43 will change as a function of the rotative position of the throttle valve. the sparlt port 43 reflecting essentially atmospheric pressure in the air inlet 44 upon closure of the throttle valve The vacuum level sensed at port 43 may be communicated through passage member It! to the vacuum reservoir I22 shown in FIG. I. With this modification incorporated into the system exhaust gas recirculation would be inhibited at small throttle openings as well as at low engine air flow for reasons which will become more apparent from the following desc riptton.

One skilled in the art will appreciate that although the engine air flow sensing mcnas 40 is described as re lating to a carburetor 4|. element 40 can also be rcferred to more generally as a throttle body since the disclosed system could be used in combination with any fuel metering system which senses air flow or in which an air flow sensor has been added.

Referring to FIG. 2 the exhaust flow responsive means 30 is shown. A housing 3| has a passage 32 formed therein to which is connected a pipe 33 from the exhaust manifold and a pipe 3-! connected to the intake manifold. Disposed within the passage 32 and fixedly secured thereto is an exhaust venturi 35. An opening 35' having a cross sectional area A, is provided in the throat of venturi 35. Housing 3| has a passage 36 disposed adjacent the opening 35' and a passage 37 lo cated upstream of the venturi 35. A valve seat 38 hasing a cros sectional area A, is formed downstream of venturi 35 in the passageway 32. Passageway J2 exhausts through an orifice 39 having a cross sectional area A. downstream of the valve seat 38. Arrow E shows the direction of recirculated exhaust gas flow An EGR valve l0 which is of standard design is fixedly secured to the housing 3] by conventional means such as bolting. The EGR valve is of the spring biased diaphragm type having a rod l2 fixedly secured to the diaphragm l3. Diaphragm l3 divides the housing ll of the EGR valve Into two separate chambers l4 and I5. chamber 14 being exposed to ambient air through an opening tnot shotsnl and chamber 15 being connected to pilot valve 2| (shown in FIG. ll through a passage l6. Valve Ill which is fixedly secured or integrally formed on the rod I2 is biased against the valve seat 38 of housing M by the spring I? which has a predetermined spring force F.. It is to be understood that as the pressure varies across the diaphragm U the rod and therefore the valve I! will move toward or away from the valve seat 38 thereby controlling the amount of exhaust gas passing through the passage 32.

One sltilled in the art will appreciate that when a venturi is used as a flow sensing element. the largest pressure differential is established by measuring the up stream pressure using a stagnation tap ie 37. and measuring the pressure at the throat of the venturi i.e. 35'. Passage member 37 which has an opening 37' senses the exhaust gas preuure S, in the passage 32 and communicates this pressure signal to the pilot valve housing 2]. and passage member 36 communicates the pressure 5, of the ehxaust gas at the opening 35 to the valve housing 2|. The differential between pressure signals S, and S inereaes with the flow rate of exhaust gas passing through the venturi 35 in a manner like the differential between atmospheric presure and S. increases with the flow rate of engine air passing through carburetor venturi 42.

Although not specifically shown. the EGR venturi 35 could be located downstream of the EOR valve l8. This approach is less desirable however. since the manifold pressure differential (which would greatly influence S and 5,) is much greater than the exhaust pressuit sensed upstream ofthe EGR valve It! thus making the control function of the pilot valve shown in FIG. I more difficult.

Referring to FIG. I the control assembly oftbe exhaust gas recirculation flow control system is shovm. Pilot valve housing 21 is of laminated construction with leclton 2lu and 2th retaining a diaphragm 60. sections 2 lb and 2liretaining diaphragms 70 and I70 and seclions 2lr and 2h! retaining a diaphragm 80 thercbeiween. These four laminated sections form a cavity 22 which because of the diaphragms and is diided into separate chambers 22a. 2211. 224'. and 22d. Disposed within cavity 22 and fixedly secured to the diaphragm 60. 70 and 80 is a pilot valve member 23. The portions of diaphragms 60. 70 and 80 which are included within the cavity 22 have "effective" cross sectional areas A... A, and A. respectively. The efl'ective" area is a function of both the outside diameter of the diaphragms and the diameter of the pressure distribution washers.

Pressure signal S, is communicated to chamber 220 by means of a passage 2la' interconnecting cavity 221 a ith the hose 37. Pressure signal S, is communicated to cavity 22h through a passage 2lb' which interconnects cavity 22b to the hose 38. Cavity 22- is subject to a pressure signal S, which is communicated to cavity 221- by means of a passage 2lr" formed in laminated section 2 1r Cavity 2241 is subiect to atmospheric pressure communicated to cavity 22d through passage 21d formed in laminated section 2ld. Cavity 22d is also connected through passage 9| to another cavity formed in lammated section 2 Id. A valve seat 92 is formed in passage 9| adjacent cavity 90. and another valve seat 93 is formed in a passage which leads into cavity 90 diainet'ical to v alve seat 92. Valve seat 93 has a cross sectional area A, A passage 94 formed in section 21d interconnects Cavity 90 to passage 16.

Another laminated section 2le of the pilot valve housing 21 is fixedly secured to laminated section 2h! \uLh that a passage 2 Ir formed therein mates with pas- \Jgt. 95. A flow restriction member H0 having a pasvage Ill therethrough is thrcadedly received in the passage 2le. Passage 2lr' opens into a reservoir I22 formed within section 2lr. Intake manifold pressure P. l\ communicated from the intake manifold 47 to the reservoir I22 by means of a hose US. A check valve l24 of standard design is disposed about the openings l2 of reservoir I22 in order to insure an adequate vacuum source regardless of variation in engine manifold JCULIm.

Pilot valve 23 which more functionally may be re lured to as a summing means is comprised essentially of three main parts. two stem portions 24 and 25 and a piston member 26. Stem portion 24 is fixedly secured to diaphragm 60 by a plurality of discs 61 and a screw o2 in a ltnown manner. Stem portion 25 is threadably received within stem portion 24 eompressively securing diaphragm 70 therebetween. Stem portion 25 has a pision chamber 7t formed therein for receiving piston member 26. Piston 26 has a flange 26' to which is mounted a plurality of discs ll and a nut 82 arranged to compressively secure diaphragm 80 to the piston 26. The top most extension of piston 26 (referring to FIG. I l is slidably disposed within chamber ll of valve stem member 25. A spring 87 having a spring force F, is disposed about stem portion 25 biasing piston 26 away from its sliding connection with stem 25. The lower most extension of piston 26 has a val e 27 fixedly secured thereto such as by i'iseting. Of course valve 27 may he integrally formed with the piston 26. Valve 27 is adapted so as to seat against either valve seat 92 or valve seat 93 as the piston 26 translates lherebctwecn. A pressure signal S, which is communicated from eavity 90 to the EGR valve [0 is a function of the relative position of piston 26 and may be magnitude equal to atmospheric or manifold pressure or in between. S, may be outside these limits under special circumstances to be described.

A cut-off valve 223 is disposed within a cavity 222 formed by laminated sections 2lb. 2lc and 2ld. Cavity 22 is divided into four chambers. chambers 222a and 222! which are divided by a diaphragm I70. chamber 222: and chamber 222d. chamber 222!) and 222r being interconnected by a passage 22h". ('ut-ofT valve 223 has a main stem portion 224 which is riveted to a plurality ofdiscs l7l compressively securing stem 224 to the diaphragm I70. The portion of diaphragm included within the chamber 222 has an effective cross sectional area A A valve member 225 is fixedly sccured to the lower most extension of the valve stem 224 in a conventional manner and is adapted to move toward and away from a valve seat 226 formed at the lower most extremity of passage 22lr" A spring reaction member 228 is threaded within the chamber 222d of the laminates. section 2ld confining a spring 227 between the valve 225 and the reaction member 228. Spring 227 has a spring force F, and is adapted to bias valve head 225 into contact with the valve seat 226. Chamber 2220 is exposed to atmospheric pressure through the passage 22!! formed in laminated section 21!). Chamber 2221'! is exposed to the pressure signal S by means ofa channel 48 formed in laminated section 211' which is adapted to receive the hose 48. (hambers 2224 and 222d are exposed to atmospheric pressure through an opening 229 in the bottom of laminated section 2M. A filter 230 is fixedly confined within the opening 229 in order to insure the purity of all air entering the cavity 222:! and the pavvage 2ft! (aviiy 2L and the passage 22h" are interconnected by passage 2h".

Referring to FIG. 4 an alternative embodiment of invention incorporating the temperature responsive member 52 is shown. The portions of the control assembly 20 which are the same as that shown in FIG I carry the same reference numerals in FIG. 4. The rivet 172 which secures the discs "I to the diaphragm I70 has an extended portion I72. A bimetallic strip 52 is fixedly secured to the laminated section 2th by a screw 54 or other conventional means. The bimetallic strip 52 is in contactive engagement with the extended portion I72 of the rivet I72. It is to be understood that the birnetal strip 52 senses the temperature in the vicnity of the control membly 20 i.e. the engine compariment temperature. and in response to a predetermined low temperature will react against the cut-off valve 223 thus terminating the communication of pressure signal S, to the chamber 22c as will be described below. Of course. other temperature responsive means could also be incorporated in this invention so that the control as sembly 20 would also be responsive to other temperature variables. as for example. the temperature of the engine coolant.

Referring to FIG 7 an alternative embodiment of the exhaust flow sensing means 30' is shown The portions of the exhaust flow sensing means 30' which are identical in structure to that shown in FIG. 2 are designated by the same reference numerals. And the new structure having equivalent functions as the parts shown in FIG. 2 are preceded by the numeral 1. An exhaust flow sensmg member I35 having an orifice I35 thcrcthrough is fixedly secured within the passage 32. The flow sensing member U5 serves the same purpose as the venturi 35 shown in FIG. 2 and the pressure S, which is sensed at the throat 35' is the same as the pressure ad acent the orifice I35. By making the cross sectional area A, equal to the cross sectional area A, of the orifice 39 shown in FIG. 2. the function of orifice 39 is performed simultaneously with the function of orifice U5. That is. the exhaust flow sensing member I35 serves the dual function of limiting EGR flow as well as sensing EGR flow.

OPERATlON phragm I70. The pressure signal 5, decreases as the en gine air flow increases through the carburetor and S, is always less than the atmospheric pressure P. which is being felt on the top side of diaphragm I70. The spring force F is strong enough to bias the cutaiff valve 223 upwardly at low engine air flows. so that the pressure S, is equal to 5,.

when the engine air flow has increased to sortie predetermined value. the pressure differential P. minus S, felt across diaphragm 80 will be sufficient to overcome spring force F, of spring 87. This will cause piston 26 of the pilot valve 23 to lift upwardly tending to close valve 27 against valve seat 92. thus making S, more a function of intake manifold pressure P. than atmospheric pressure P.. The pressure signal S, is communicated to chamber ofthe EGR valve 10. causing diaphragm l. to react against the spring force F, of spring 17 thereby o ening valve lll causing exhaust gas to flow through venturi 35. The EUR flow through venturi produces a differential pressure 5, minus 5,. Since these two pressure signals are communicated to both sides of diaphragm of the pilot valve 23. and since S, is less than S, a downward force is developed on the diaphragm 60. An additional component of downward force is caused by the pressure differential S, less S acting on the diaphragm 70. This causes a further compression of the spring 87. and the pilot valve assembly 23 through the three diaphragms 60. and acts as though rigidly attached to a common stern. If the EGR flow becomes excessive. the pressure differential S, minus S will cause a force unbalance on diaphragm 60 thereby tending to force valve 27 into contact with valve seat 93 which in turn admits atmospheric pressure P, to the EGR valve chamber l5; this in turn causes valve 18 to move toward valve seat 38 thereby cutting EGR flow. The forces reacting on diaphragm I3 of the EGR valve l0 therefor. tend either to adjust the relative open or closed position of valve ll.

As the engine air flow continues to increase and S, continues to decrease valve 27 continues to move upwardly. Simultaneously. the balance of forces on the pilot valve 23 demand a corresponding increase in the pressure differential S, minus 5.. since the further opening of valve It! causes an increase in EGR flow. Thus. the pilot valve will maintain a position to control the EGR flow in an increasing relationship to the increasing engine air flow. If the effective area A. of dia phragm 60 is equal to the effective area A. of the diaphragm 80 and if also the areas A, and A, are sufficiently small. the EGR flow will be in direct proportion to the engine air flow.

Alternatively. the cross sectional areas A, and A, of diaphragm 70 and passage respectively. or an additional spring (not shown] can be used with the effect of exhaust back pressure and intake manifold pressure. to produce a scheduled relationship between the EGR flow and the engine air flow which depart from proportionality. The system amounts to a closed loop control having its set point varied by means of other sensed variables. It is to he understood that the control assembly 20 is a means for summing the pressure signals S. and S, so that the amount of recirculated exhaust gas entering the intake manifold varies in a modifiable proportiunal relationship to engine air flow.

When the EGR flow becomes limited by the effect of orifice 39. the pressure differential 5, minus 5, can no longer adjust to satisfy the force balance on the pilot valve 23. The pilot valve will then cause valve 27 to be seated against valve seat 92 causing S, to equal P. Under these conditions reservoir I22 can be effective to maintain a vacuum on the EGR valve l0 that l. higher than the engine manifold vacuum. This pcfrttlls designing the EGR valve to operate at substantial \acuum levels while still having the capability of delivering EGR flow at very low manifold vacuums. That is. the combination of the reservoir I22 and the check valve I24 maintain an adequate vacuum source regardless of variations in engine manifold vacuum and regardless of whether the reservoir is controlled by spark port pres sure or by manifold pressure. Although orifice .W with cross sectional area A. is not essential. unless such an orifice is used. the flow of EGR would continue to in crease with increasing air flow until the point of cut-oft is reached.

As the engine air flow continues to increase. the EGR flow will increase only slightly owing to the increase in exhaust baclt pressure. At a point determined by the spring force F, of the spring 227 the pressure dro across diaphragm will be large enough to close cutoff valve 223. That is. valve member 235 which is sccured to the valve stem 224 of the cut-off valve 223 will seat against the valve seat 236 formed at the upper end of passage 22k and valve 225 will be released from valve seat 226 allowing atmospheric pressure to be communicated through passage 22 lr' and passage 21" to chamber 22:. Since S will then equal P.. the force balance on diaphragm B0 shifts the position of valve 27 into contact with valve seat 93 so that S, becomes equal to P. thereby closing EGR valve 10.

By modifying and changing the various design parameters shown herein and for example. by using the spark port pressure of the carburetor 40 instead of the intake manifold pressure P. in the reservoir 122. different criteria for affecting cut-in" and "cut-off of EUR flovcan be accomplished.

As was described above the temperature responsive element 52 as shown in FIG. 4 can be caused to react on the stern of cut-off valve 223 making the system responsive to low and/or high ambient or engine compartment temperature in order to inhibit the EGR flow when either of these conditions may exist. That is. as the engine compartment temperature decreases a predetermined temperature is eventually reached which it ill cause the bimetalic strip to bend downwardly in the direction of arrow T shown in FIG. 4 forcing the valve stem 223 downwardly cutting off the pressure signal 5,. l'his means that atmospheric pressure is communicated to chamber 12: forcing steni 26 downwardly which in turn admits atmospheric pressure to the EGR valve l0.

Flow restriction member H0 shown in FIG. 1 serves the purpose of limiting the flow of air into the intake manifold so as to avoid creating air fuel ratio errors which might occur if any large amount of fresh air were allowed to bypass the carburetor into the intake manifold. Note. that any time valve 17 is between its two valve seats. there is a continuous flow of fresh air through passage Zld'. channel 91. and cavity I21. etc. into the intake manifold. Means to prevent this air flow from having the noted adverse effect is important to the overall system.

Referring to FIG. 6 actual test results are graphically illustrated. Lines A and C represent plots of an EGR s)slt.'m designed for EGR flows of exactly Ill and 30 percent of the engine air flow respectively. Line 8 is a plot of the disclosed system wherein intake manifold vacuum varied substantially between 6 and i4 inches of mercury it is important to note that all the objects of the invention are accomplished. since EGR is inhibited at low and at high engine air flows. and EGR flow begins smoothly and flows at a relatively constant or scheduled fraction of the engine air flow.

While only one preferred embodiment and two forms of alternative embodiments of the inventive system have been disclosed. it will be apparent to those skilled in the art that changes may be made to the invention .is set forth in the appended claims and in some instances certain features of the invention may be used to advantage without corresponding use of other features. For example. it was pointed out that control of the pilot valve 23 can be easily modified by changing certain of the design parameters. and certain of the pressure sensitive cavities contained in the housing 2! may sense pressures other than those specifically decribed. Also. on a qualitative basis pilot valve 23 could control the EGR flow directly. However. since the venluri vacuum signals are relatively low and since the EGR valve must have significant area. this approach would require very large diaphragm and would thus be impractical. Accordingly. it is intended that the illustrative and descriptive materials herein be used to illustrate the principles of the invention and not to limit the scope thereof.

I claim:

I. In an exhaust gas recirculation flow control system for an internal combustion engine having valve means disposed within the recirculated exhaust gas passage. thc improvement comprising:

means for generating a first differential pressure responsive to engine air flow; means for generating a second differential pressure responsive to recirculated exhaust gas flow; and

means for summing said first and second differential pressures and operative to regulate the relative opening and closing of said valve means so that the volume of exhaust gas being recirculated varies in .i proportional relationship in engine atr flou 2. The combination as claimed in claim I and including further means for tenninating the communication of said first pressure signal to said summation means when engine air flow has increased to a predetermined value.

3. The combination as claimed in claim I and including further means for terminating the communication of said first pressure signal to said summation means when the engine compartment temperature reaches a predetermined value.

4. The combination as claimed in claim I including further biasing means operative with said summation means for maintaining said valve means in a closed position until engine air flow reaches a predetermined minimum value.

5. In combination with an internal combustion engine having passage means for recirculating exhaust gas to the intake manifold an exhaust gas recirculation flow control system comprising:

engine air flow sensing means responsive to a predetermined range of volumetric air passing therethrough and operative to provide a first pressure signal related to said air flow.

first pressure sensitive means responsive to first pressure signal; exhaust flow sensing means responsive to a predetermined range of volumetric exhaust gas passing thcrethrough and operative to provide a second pressure signal related to exhaust gas flow;

second pressure sensitive means responsive to said second pressure signal;

first valve means operatively disposed in the exhaust gas passage means so as to regulate the amount of exhaust gas entering the engines intake manifold. and

second valve means operatively interconnecting said first and second pressure sensitive means so that said first and second pressure signals act to control the relative position of said first valve means.

6. The combination as claimed in claim 5 wherein said second valve means is operative to move between a first port and a second port. said first port being exposed to ambient air and said second port being exposed to intake manifold vacuum.

7. The combination as claimed in claim 5 including further third valve means operatively disposed between said engine air flow sensing means and said second valve means. said third valve means being operative to move between a first position wherein said first pressure signal is communicated to said second valve me ans and second position wherein ambient air is communicated to said second valve means.

I. The combination as claimed in claim 7 including further a temperature responsive member operatively connected to said third valve means to control its relative position under predetermined temperature conditions.

9. Use combination as claimed in claim 7 wherein said third valve means includes a third pressure sensitive means. said pressure sensitive means being exposed to said first pressure signal on side thereof and to ambient air on the other side thereof.

[0. The combination as claimed in claim 5 including further at least one carburetor for providing an air fuel mixture to the engine. said carburetor having at least one venturi therein It. The combination as claimed in claim 10 wherein the engine air flow sensing means includes an opening in the throat of said carburetor venturi. and passage means for communicating the pressure at said opening to said first pressure sensitive means.

II. The combination as claimed in claim 5 wherein said exhaust flow sensing means includes a venturi disposed in the exhaust gas passage means. said venturi having an opening in the throat thereof; and

passage means operative to communicate the pressure at said opening to said second pressure sensitive means.

IS. The combination as claimed in claim 5 wherein said exhaust f'losv sensing means includes a flow sensing element disposed within the exhaust gas passage means. said floss sensing element having an opening therethrough; and

passage means operative to communicate the pressure at said opening to said second pressure sensitive means.

l4. In combination with an internal combustion engine having exhaust gas passage means for recirculating exhaust gas to the engine intake manifold. an exhaust gas recirculation flow control ssstem comprising:

engine air flow responsive means operative to provide a first differential pressure related to engine air flow.

exhaust gas flow responsive means operative to provide a second differential pressure related to exhaust gas flo and means for summing said first and second differential pressures and operative to regulate the amount of exhaust gas being recirculated to the engine's intake manifold so that the volume of exhaust gas being recirculated varies in a modifiable proportional relationship to engine air flow.

IS. The combination as claimed in claim l4 wherein said summing means includes a piston member which moves between a first port and a second port. said first ort being exposed to ambient air pressure and said second port being exposed to intake munlfold vacuum.

to. The combination as claimed in claim 14 wherein \Jld summing means includes a piston member which moves between a first port and a second port. said first port being exposed to ambient air pressure. and said \CCtmd port being exposed to carburetor spark port acuum.

IT. The combination as claimed in claim 14 including further passage means for communicating said first pressure signal to said summing means; and

valve means operatively disposed in said passage means such that it controls the communication of said first pressure signal to said summing means.

l8. The combination as claimed in claim [7 including further temperature responsive means operatively connected to said valve means such that said first pressure signal is prevented from reaching said summing means when a predetermined temperature condition is l2 reached.

19. In an exhaust gas recirculation flow control s vstem for an internal combustion engine having valve means disposed vvithin the recirculated exhaust gas pas- 5 sage. the improvement comprising:

means for generating a first pressure signal responsise to engine air fiovv; means for generating a second pressure signal responsive to recirculated exhaust gas flow; means for summing said first and second pressure signals and operative to regulate the relative opening and closing of said valve means so that the volume of exhaust gas being recirculated varies in a proportional relationship to engine air flovv; and means for terminating the communication of said first pressure signal to said summation means when the engine compartment temperature reaches a predetermined value. 20. In combination with an internal combustion en- :o gine having exhaust gas passage means for recirculating exhaust gas to the engine intake manifold. an exhaust gas recirculation flow control system comprising:

engine air flow responsive means operative to provide a first pressure signal related to engine air flow; exhaust gas flovv responsive means operative to provide a second pressure signal related to exhaust gas flow. and means for summing said first and second pressure signals and operative to regulate the amount of exhaust gas being recirculated to the engine's intake manifold so that the volume of exhaust gas being recirculated varies in a modifiable proportional relationship to engine air flosv. said summing means includes a piston member which moves between a first port and a second port. said first port being exposed to ambient air pressure and said second port being exposed to intake manifold vacuum. 2|. In combination with an internal combustion engine having exhaust gas passage means for recirculating exhaust gas to the engine intake manifold. an exhaust gas recirculation flow control s)stem comprising:

engine air flow responsive means operative to provide a first pressure signal related to engine air flow. exhaust gas flow responsive means operative to provide a second pressure signal related to exhaust gas flow; and means for summing said first and second pressure signals and operative to regulate the amount of exhaust gas being recirculated to the engine's intake manifold so that the volume of exhaust gas being recirculated varies in a modifiable proportional relationship to engine air flow. said summing means includes a piston member which moves between a first port and a second port. said first port being exposed to ambient air pressure. and said second port being exposed to carburetor spark port vacuum.

O O O O Q Jli 

1. In an exhaust gas recirculation flow control system for an internal combustion engine having valve means disposed within the recirculated exhaust gas passage, the improvement comprising: means for generating a first differential pressure responsive to engine air flow; means for generating a second differential pressure responsive to recirculated exhaust gas flow; and means for summing said first and second differential pressures and operative to regulate the relative opening and closing of said valve means so that the volume of exhaust gas being recirculated varies in a proportional relationship to engine air flow.
 2. The combination as claimed in claim 1 and including further means for terminating the communication of said first pressure signal to said summation means when engine air flow has increased to a predetermined value.
 3. The combination as claimed in claim 1 and including further means for terminating the communication of said first pressure signal to said summation means when the engine compartment temperature reaches a predetermined value.
 4. The combination as claimed in claim 1 including further biasing means operative with said summation means for maintaining said valve means in a closed position until engine air flow reaches a predetermined minimum value.
 5. In combination with an internal combustion engine having passage means for recirculating exhaust gas to the intake manifold an exhaust gas recirculation flow control system comprising: engine air flow sensing means responsive to a predetermined range of volumetric air passing therethrough and operative to provide a first pressure signal related to said air flow; first pressure sensitive means responsive to said first pressure signal; exhaust flow sensing means responsive to a predetermined range of volumetric exhaust gas passing therethrough and operative to provide a second pressure signal related to exhaust gas flow; second pressure sensitive means responsive to said second pressure signal; first valve means operatively disposed in the exhaust gas passage means so as to regulate the amount of exhaust gas entering the engine''s intake manifold; and second valve means operatively interconnecting said first and second pressure sensitive means so that said first and second pressure signals act to control the relative position of said first valvE means.
 6. The combination as claimed in claim 5 wherein said second valve means is operative to move between a first port and a second port, said first port being exposed to ambient air and said second port being exposed to intake manifold vacuum.
 7. The combination as claimed in claim 5 including further third valve means operatively disposed between said engine air flow sensing means and said second valve means, said third valve means being operative to move between a first position wherein said first pressure signal is communicated to said second valve means and second position wherein ambient air is communicated to said second valve means.
 8. The combination as claimed in claim 7 including further a temperature responsive member operatively connected to said third valve means to control its relative position under predetermined temperature conditions.
 9. The combination as claimed in claim 7 wherein said third valve means includes a third pressure sensitive means, said pressure sensitive means being exposed to said first pressure signal on side thereof and to ambient air on the other side thereof.
 10. The combination as claimed in claim 5 including further at least one carburetor for providing an air fuel mixture to the engine, said carburetor having at least one venturi therein.
 11. The combination as claimed in claim 10 wherein the engine air flow sensing means includes an opening in the throat of said carburetor venturi, and passage means for communicating the pressure at said opening to said first pressure sensitive means.
 12. The combination as claimed in claim 5 wherein said exhaust flow sensing means includes a venturi disposed in the exhaust gas passage means, said venturi having an opening in the throat thereof; and passage means operative to communicate the pressure at said opening to said second pressure sensitive means.
 13. The combination as claimed in claim 5 wherein said exhaust flow sensing means includes a flow sensing element disposed within the exhaust gas passage means, said flow sensing element having an opening therethrough; and passage means operative to communicate the pressure at said opening to said second pressure sensitive means.
 14. In combination with an internal combustion engine having exhaust gas passage means for recirculating exhaust gas to the engine intake manifold, an exhaust gas recirculation flow control system comprising: engine air flow responsive means operative to provide a first differential pressure related to engine air flow; exhaust gas flow responsive means operative to provide a second differential pressure related to exhaust gas flow; and means for summing said first and second differential pressures and operative to regulate the amount of exhaust gas being recirculated to the engine''s intake manifold so that the volume of exhaust gas being recirculated varies in a modifiable proportional relationship to engine air flow.
 15. The combination as claimed in claim 14 wherein said summing means includes a piston member which moves between a first port and a second port, said first port being exposed to ambient air pressure and said second port being exposed to intake manifold vacuum.
 16. The combination as claimed in claim 14 wherein said summing means includes a piston member which moves between a first port and a second port, said first port being exposed to ambient air pressure, and said second port being exposed to carburetor spark port vacuum.
 17. The combination as claimed in claim 14 including further passage means for communicating said first pressure signal to said summing means; and valve means operatively disposed in said passage means such that it controls the communication of said first pressure signal to said summing means.
 18. The combination as claimed in claim 17 including further temperature responsive means operatively connected to said valve means such that said first pressure signal is prevented from reaching said summing means when A predetermined temperature condition is reached.
 19. In an exhaust gas recirculation flow control system for an internal combustion engine having valve means disposed within the recirculated exhaust gas passage, the improvement comprising: means for generating a first pressure signal responsive to engine air flow; means for generating a second pressure signal responsive to recirculated exhaust gas flow; means for summing said first and second pressure signals and operative to regulate the relative opening and closing of said valve means so that the volume of exhaust gas being recirculated varies in a proportional relationship to engine air flow; and means for terminating the communication of said first pressure signal to said summation means when the engine compartment temperature reaches a predetermined value.
 20. In combination with an internal combustion engine having exhaust gas passage means for recirculating exhaust gas to the engine intake manifold, an exhaust gas recirculation flow control system comprising: engine air flow responsive means operative to provide a first pressure signal related to engine air flow; exhaust gas flow responsive means operative to provide a second pressure signal related to exhaust gas flow; and means for summing said first and second pressure signals and operative to regulate the amount of exhaust gas being recirculated to the engine''s intake manifold so that the volume of exhaust gas being recirculated varies in a modifiable proportional relationship to engine air flow, said summing means includes a piston member which moves between a first port and a second port, said first port being exposed to ambient air pressure and said second port being exposed to intake manifold vacuum.
 21. In combination with an internal combustion engine having exhaust gas passage means for recirculating exhaust gas to the engine intake manifold, an exhaust gas recirculation flow control system comprising: engine air flow responsive means operative to provide a first pressure signal related to engine air flow; exhaust gas flow responsive means operative to provide a second pressure signal related to exhaust gas flow; and means for summing said first and second pressure signals and operative to regulate the amount of exhaust gas being recirculated to the engine''s intake manifold so that the volume of exhaust gas being recirculated varies in a modifiable proportional relationship to engine air flow, said summing means includes a piston member which moves between a first port and a second port, said first port being exposed to ambient air pressure, and said second port being exposed to carburetor spark port vacuum. 